Aircraft with a turbine engine compressor output hot air. Heat exchangers can bleed this hot air over stacks of fins and thereby control the environmental temperature in aircrafts and also increase efficiency of the engine. Each fin measures generally below 0.3 mm in thickness and is shaped to maximize the surface-to-volume ratio. The fins are typically brazed on a base metal at a temperature above about 1040° C., after which the fin stacks are welded to the aircraft. Since the fins undergo thermal cycles during operation, they are expected to show adequate resistance to thermal fatigue. One way to increase the resistance to thermal fatigue is to employ thicker fins. However, thicker fins may add undesirable weight to the aircraft and decrease the thermal conductance.
Current materials for heat exchangers can withstand only a limited range of temperature. For example, solid-solution-strengthened commercial nickel-based alloys such as Inconel 625, with a nominal composition of 21 Cr, less than 5 Fe, 3.7 Nb, 1 Co, less than 0.5 Mn, less than 0.5 Si, 0.4 Ti, less than 0.4 Al, less than 0.1 C, and the balance Ni, in wt %, show low resistance to creep and low thermal conductivity at high temperatures. Other alloys such as Haynes® 282®, with a nominal composition of 20 Cr, 10 Co, 8.5 Mo, 2.1 Ti, 1.5 Al, 1.5 Fe, 0.3 Mn, 0.15 Si, 0.06 C, 0.005 B, and the balance Ni, in wt %, are strengthened by L12-Ni3(Al, Ti) precipitates. Precipitation-strengthened alloys generally have a lower solute content in the matrix compared to solid-solution-strengthened alloys. This can result in less distortion of the crystal lattice of the matrix and therefore higher thermal conductivity. However, the higher contents of Al and Ti required for the L12 precipitation can also undesirably promote oxide formation during brazing, resulting in ineffective wetting of the braze alloy on the base metal and a poor braze quality.